107 lines
4.1 KiB
Rust
107 lines
4.1 KiB
Rust
use bootloader::bootinfo::{MemoryMap, MemoryRegionType};
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use x86_64::{
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structures::paging::{
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FrameAllocator, Mapper, OffsetPageTable, Page, PageTable, PhysFrame, Size4KiB,
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UnusedPhysFrame,
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},
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PhysAddr, VirtAddr,
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};
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/// Initialize a new OffsetPageTable.
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///
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/// This function is unsafe because the caller must guarantee that the
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/// complete physical memory is mapped to virtual memory at the passed
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/// `physical_memory_offset`. Also, this function must be only called once
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/// to avoid aliasing `&mut` references (which is undefined behavior).
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pub unsafe fn init(physical_memory_offset: VirtAddr) -> OffsetPageTable<'static> {
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let level_4_table = active_level_4_table(physical_memory_offset);
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OffsetPageTable::new(level_4_table, physical_memory_offset)
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}
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/// Returns a mutable reference to the active level 4 table.
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///
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/// This function is unsafe because the caller must guarantee that the
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/// complete physical memory is mapped to virtual memory at the passed
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/// `physical_memory_offset`. Also, this function must be only called once
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/// to avoid aliasing `&mut` references (which is undefined behavior).
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unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static mut PageTable {
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use x86_64::registers::control::Cr3;
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let (level_4_table_frame, _) = Cr3::read();
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let phys = level_4_table_frame.start_address();
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let virt = physical_memory_offset + phys.as_u64();
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let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
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&mut *page_table_ptr // unsafe
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}
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/// Creates an example mapping for the given page to frame `0xb8000`.
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pub fn create_example_mapping(
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page: Page,
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mapper: &mut OffsetPageTable,
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frame_allocator: &mut impl FrameAllocator<Size4KiB>,
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) {
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use x86_64::structures::paging::PageTableFlags as Flags;
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let frame = PhysFrame::containing_address(PhysAddr::new(0xb8000));
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// FIXME: ONLY FOR TEMPORARY TESTING
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let unused_frame = unsafe { UnusedPhysFrame::new(frame) };
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let flags = Flags::PRESENT | Flags::WRITABLE;
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let map_to_result = mapper.map_to(page, unused_frame, flags, frame_allocator);
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map_to_result.expect("map_to failed").flush();
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}
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/// A FrameAllocator that always returns `None`.
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pub struct EmptyFrameAllocator;
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unsafe impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
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fn allocate_frame(&mut self) -> Option<UnusedPhysFrame> {
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None
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}
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}
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/// A FrameAllocator that returns usable frames from the bootloader's memory map.
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pub struct BootInfoFrameAllocator {
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memory_map: &'static MemoryMap,
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next: usize,
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}
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impl BootInfoFrameAllocator {
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/// Create a FrameAllocator from the passed memory map.
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///
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/// This function is unsafe because the caller must guarantee that the passed
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/// memory map is valid. The main requirement is that all frames that are marked
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/// as `USABLE` in it are really unused.
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pub unsafe fn init(memory_map: &'static MemoryMap) -> Self {
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BootInfoFrameAllocator {
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memory_map,
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next: 0,
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}
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}
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/// Returns an iterator over the usable frames specified in the memory map.
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fn usable_frames(&self) -> impl Iterator<Item = UnusedPhysFrame> {
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// get usable regions from memory map
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let regions = self.memory_map.iter();
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let usable_regions = regions.filter(|r| r.region_type == MemoryRegionType::Usable);
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// map each region to its address range
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let addr_ranges = usable_regions.map(|r| r.range.start_addr()..r.range.end_addr());
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// transform to an iterator of frame start addresses
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let frame_addresses = addr_ranges.flat_map(|r| r.step_by(4096));
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// create `PhysFrame` types from the start addresses
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let frames = frame_addresses.map(|addr| PhysFrame::containing_address(PhysAddr::new(addr)));
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// we know that the frames are really unused
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frames.map(|f| unsafe { UnusedPhysFrame::new(f) })
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}
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}
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unsafe impl FrameAllocator<Size4KiB> for BootInfoFrameAllocator {
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fn allocate_frame(&mut self) -> Option<UnusedPhysFrame> {
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let frame = self.usable_frames().nth(self.next);
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self.next += 1;
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frame
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}
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}
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